Photosynthetic traits and plant hydraulic dynamics in Gamhong apple cultivar under drought, waterlogging, and stress recovery periods

Drought and waterlogging are major abiotic stresses in fruit cultivation that should both be considered when establishing an orchard as the frequency and severity of extreme climate events continue to rise. This study investigated the photosynthetic traits and plant-water relations of Gamhong/M.9 apple cultivar during and after drought (DT) and waterlogging (WT) treatments. Both stresses adversely affected the photosynthetic and plant hydraulic traits, with stress-specific effects. Drought significantly increased the leaf mass per area, indicating that the cultivar allocated more resources to structural investment than to photosynthesis upregulation. The net photosynthetic rate and stomatal conductance were reduced at an earlier stage under DT (day 3) than under WT (day 6). The recovery of these photosynthetic traits was slower under DT than that under WT, with the net photosynthetic rate recovering 12 days after DT and 9 days after WT, whereas the stomatal conductance recovered 11 days after DT and 7 days after WT. Additionally, the progressive increase in xylem sap abscisic acid concentration resulted in a linear decrease in stomatal conductance, with a greater under DT than under WT. The leaf water potential and sap flow followed similar decreasing trends as that of the photosynthetic traits; however, hydraulic traits recovered earlier than photosynthetic traits under both stress conditions. The leaf water potential was reduced on day 4 of DT and recovered 6 days after watering was resumed. Contrastingly, under WT, this trait was reduced on day 7 of the treatment and recovered 4 days after its end. Our findings highlight that the Gamhong cultivar has higher acclimation potential to waterlogging and can alleviate the adverse effects of excess water while maintaining its physiological traits and improving plant-water relations.